Hypertension is associated with decreased endothelium-dependent vasodilation. However, whether endothelial dysfunction is a cause or a consequence of elevated blood pressure is unknown. Therefore, to determine whether hypertension can directly induce endothelial dysfunction, we investigated the effect of increases in intra-arterial pressure on endothelium-dependent vasodilation of the human microvasculature. Small arteries (internal diameter: 202+/-75 microns) were isolated from gluteal fat biopsies in 12 healthy normotensive subjects (8 men and 4 women; age: 46+/-10 years). Arteries were cannulated and perfused in chambers oxygenated at 37 C. Endothelium-dependent and -independent responses to acetylcholine (Ach;10-9 to 10-4 M) and sodium nitroprusside (SNP; 10-9 to 10-4 M), respectively, were obtained after incubating the vessel with incremental intra-vascular pressures of 50, 80, and 120 mmHg for 60 min each. The response to Ach was also obtained in different arteries after 3 consecutive incubation periods at 50 mmHg. Arterial internal diameter was measured directly from amplified digital images. A significant reduction in the vasodilator response to Ach was observed with increases in intra-vascular pressure (mean vasodilation: 62%, 49%, and 26% at 50, 80, and 120 mmHg, respectively; P<0.001). In contrast, the response to SNP showed a non-significant trend toward greater vasodilation with increases in pressure (mean vasodilation: 40%, 52%, and 57% at 50, 80, and 120 mmHg, respectively; P=0.10). There was no difference in the consecutive dose-response curves to Ach obtained at the same intra-vascular pressure (mean vasodilation: 48%, 46%, and 49%; P=0.61). Transient increases in intra-vascular pressure significantly depress endothelium-dependent vasodilation in human resistance arteries. These findings suggest that elevated blood pressure per se may cause endothelial dysfunction in humans and have implications for the pathophysiology of endothelial dysfunction in hypertension.